Cable conveying apparatus and method

ABSTRACT

A cable conveying apparatus and method installs a cable in conduit by the application of a pushing force generated by a drive assembly. The speed of the cable and the speed of the drive assembly are monitored wherein the drive assembly is shut off when the drive assembly and cable speeds exceed a predetermined difference. The cable conveying apparatus includes a blower, and a missile attached to the lead end of the cable, wherein the missile sealably and slideably engages the conduit such that the blower and missile combine to generate a pull force on the cable which cooperates with the pushing force of the drive assembly so as to install the cable in the conduit. The cable conveying apparatus also includes a high speed cable shut off system, and a low speed cable shut off system. The drive assembly includes two opposed continuous chains each including a plurality of cable engaging pads, and each driven by a hydraulic motor. A hydraulic cylinder preferably holds the drive chains at a spaced apart distance.

This application is a Divisional of application Ser. No. 08/923,361,filed Sep. 4, 1997, which application(s) are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for installingcable, such as fiber optic communications cable, in duct or otherconduit, such as underground duct.

BACKGROUND OF THE INVENTION

Various techniques are known for installing cable in duct or otherconduit, which can be underground, above ground or in buildings.Sometimes the underground duct is known as “innerduct.” A firsttechnique is to pull the cable through conduit with a previouslypositioned wire or string attached to a lead end of the cable.

The use of high speed moving air to drag a lightweight and flexibleoptical fiber member through the conduit is also known, such asdescribed in U.S. Pat. No. 4,691,896, to Reeves et al. According toReeves et al., the high speed air creates a fluid drag force distributedalong the optical fiber member in order to pull the optical fiber memberthrough the conduit.

U.S. Pat. Nos. 4,850,569 and 4,934,662 to Griffioen et al. describecombining high speed air flow with a pushing force applied at the entryend of the conduit to install the cable. U.S. Pat. Nos. 5,197,715 and5,474,277 to Griffioen further describe the use of a leaky missileattached to the lead end of the cable which adds a tension force on thelead end of the cable, in addition to the motive forces applied to thecable via the high speed moving air.

The use of pressurized air in combination with a sealed missile,parachute or other device for creating a pressure difference at the leadend of the cable is also known. The pressure difference creates apushing force on the missile or other device, which pulls the lead endof cable through the conduit.

Various concerns arise when cable is installed in conduit. One concernis the ease of installation. A further concern is avoidance of damage tothe cable during installation. Damage can occur in a variety of waysincluding: 1) crushing the cable with the installation equipment in thediametral direction; 2) causing the cable to have bending damage orcolumn damage (may be referred to as “accordion damage”) due to anexcessive force applied in the longitudinal direction; and 3) damagingthe protective cable jacket, such as by wearing, shredding or cuttingthe outer protective layer. Another concern is to minimize the amount oftime needed to install the cable. Also, there is a concern to avoidsplices in the cable as much as possible. Splices are time consuming tomake, and may lead to a decrease in cable performance. Therefore, it isdesirable to install the longest continuous length of cable possible toreduce the number of splices needed for the desired cable run.

There is a need in the prior art for further systems and methods whichaddress the above-identified concerns, and other concerns.

SUMMARY OF THE INVENTION

The present invention concerns an apparatus for conveying a cable, suchas through a conduit, in order to install the cable in the conduit. Theapparatus is useful for installing fiber optic cable in undergroundduct, for example. A cable drive assembly frictionally engages anoutside surface of the cable and applies a pushing force on the cablefor insertion of the cable into the conduit. A drive assembly speedsignal generator and a cable speed signal generator produce signalsprocessed by a control system. Cable speed and drive assembly speed aremonitored by the control system such that if the drive assembly exceedsa predetermined faster speed relative to the cable, the drive assemblywill be stopped. Monitoring relative speeds is particularly useful inpreventing cable jacket damage, such as might occur if the driveassembly is slipping and moving too fast relative to the cable, or whenthe cable has stopped due to an obstruction in the conduit, causingcolumn or accordion damage.

Preferably, the cable drive assembly is used in combination with a cableblower assembly, and a sealed missile sealably and slideably engagedwith an inner wall surface of the conduit. The cable blower and themissile create a pressure difference at the lead end of the cable,thereby creating a pull force on the cable. The combination of the cabledrive assembly, and the missile and the cable blower assembly permitsconvenient installation of the cable in conduit, such as undergroundduct.

Preferably, the control system includes a high speed cable shut offsystem, and a low speed cable shut off system, both of which shut offthe drive assembly when the speed of the cable either exceeds a certainpredetermined maximum, or falls below a certain predetermined minimum.

In the preferred embodiment, the cable drive assembly includes twoopposed tractor drive assemblies, each including a continuous chain anda plurality of cable engaging pads made from plastic and mounted to thechain. Preferably, the tractor drive assemblies are driven by hydraulicmotors. In the preferred embodiment, the tractor drive assemblies arepositioned at a predetermined spaced apart distance, and place apredetermined pressure on the cable, by the use of a hydraulic clampcylinder. The clamp cylinder moves one tractor drive assembly toward andaway from the other tractor drive assembly, as desired by the operator.The clamp cylinder allows a desired normal force to be placed on thecable by the tractor drive assemblies, so as to apply the properfrictional force to drive the cable forward, and yet not exceed thecompressive limits of the cable. Hydraulics allow such normal force tobe preset, and consistently repeated during operation.

The present invention also relates to a method of installing cable in aconduit including the steps of providing a drive assembly for moving thecable in a forward direction, generating a first signal indicative ofmovement of the drive assembly, and generating a second signalindicative of movement of the cable. The method further includes thesteps of comparing the first and second signals over time, andgenerating a drive assembly shut off signal if relative speeds of thedrive assembly and the cable exceed a predetermined difference. Themethod preferably includes providing the cable with a sealed missilesealably and slideably engaged with an inner wall of the conduit, andfurther applying air pressure to the missile so as to cause the missileto generate a pull force on the cable. The method also preferablyincludes monitoring cable high speed and low speed conditions, andgenerating a drive assembly shut off signal if the cable speed exceeds apredetermined maximum or falls below a predetermined minimum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a cable conveying apparatus inaccordance with the present invention showing cable being installed intoa duct with the apparatus.

FIG. 2 is a perspective view of an embodiment of the cable conveyingapparatus in accordance with the present invention.

FIG. 3 is a top view of the apparatus shown in FIG. 2.

FIG. 4 is a front view of the apparatus shown in FIG. 2, with a portionof the housing removed.

FIG. 5 is a back view of the apparatus shown in FIG. 2, with portions ofthe housing removed.

FIG. 6 is an end view of the apparatus shown in FIG. 2.

FIG. 7 is a perspective view of the lower tractor drive assembly of theapparatus shown in FIG. 2.

FIG. 8 is an exploded perspective view of the lower tractor driveassembly.

FIG. 9 is a perspective view of the upper tractor drive assembly of theapparatus shown in FIG. 2.

FIG. 10 is an exploded view of the upper tractor drive assembly.

FIG. 11 is an enlarged perspective view of one of the chain pads.

FIG. 12 is a perspective view of the cable counter assembly of theapparatus shown in FIG. 2.

FIG. 13 is an exploded view of the cable counter assembly.

FIG. 14 is an exploded perspective view of portions of the air blockassembly of the apparatus shown in FIG. 2.

FIG. 15 is an exploded perspective view of portions of the duct mountassembly of the apparatus shown in FIG. 2.

FIG. 16 is an exploded perspective view of the adjustment assembly forthe air block assembly and the duct mount assembly of FIGS. 14 and 15.

FIG. 17 shows the air block assembly and the duct mount assembly withthe cable and the duct in place, and the upper block of the air blockassembly removed.

FIG. 18 shows the air block assembly and the duct mount assembly withthe upper block portions of each removed, and no duct or cable present.

FIG. 19 is a schematic representation of the cable speed control systemof the apparatus shown in FIG. 2.

FIG. 20 is a schematic representation of the hydraulic control system ofthe apparatus shown in FIG. 2.

FIG. 21 is a perspective view of the frame of the apparatus shown inFIG. 2.

FIG. 22 is a perspective view of the frame of FIG. 21 including portionsof the control system.

FIG. 23 is a bottom view of the frame and control system features shownin FIG. 22.

FIG. 24 is a side view of an embodiment of a missile usable with thecable conveying apparatus of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention generally concerns a cable conveying apparatus andmethod which generates a motive force and applies the force to a cablefor use in installing the cable in a conduit Preferably, the motiveforce is a pushing force developed by a drive assembly whichfrictionally engages the cable at the entry end of the conduit. Thecable conveying apparatus and method of the present invention preferablygenerates a further motive force on the cable by blowing a missileattached to an end of the cable through the conduit. Such motive pullingforce in combination with the motive pushing force from the driveassembly can be utilized to install cable, such as fiber optic cable, induct or other conduit, such as underground innerduct.

By monitoring the motive forces and the speeds of the system components,damage to the cable is reduced or avoided, and a properly performingcable can be installed. For example, compressive force damage in thediametral direction of the cable (“crushing”) and column damage can bereduced or avoided by monitoring the normal force applied by the cabledrive assembly. By also monitoring the speeds of the cable driveassembly and the cable, it is also possible to reduce or avoid cablejacket damage such as might occur if the cable drive assembly isslipping on the cable and moving faster than the cable, as when thecable begins to slow down in the case of an impending stoppage. Thecable is further protected by monitoring cable speed in the case ofexcessively high cable speed, or too low of a cable speed. Runawaycable, such as in the case of excessively high speed, is not desired,nor is too low of a speed, which may be indicative of an instant cablestoppage.

The present invention reduces the risk of cable damage, such as canoccur if excessive normal forces, excessive cable slippage, andexcessively high or too low speeds of the cable are not properlymonitored or avoided. Through automatic monitoring and control,advantageous apparatus and methods result, thereby allowing improvedsuccess rates for cable installation. Also, through automatic monitoringand control, less experienced installers can more consistently installthe cable.

Turning now to FIGS. 1-6, a schematic representation (FIG. 1), and anexample embodiment (FIGS. 2-6) for a cable conveying apparatus 20 inaccordance with the invention are shown. FIGS. 7-24 show components ofapparatus 20 in greater detail. Apparatus 20 generates motive force(s)for the installation of cable 22 to be pulled from reel 24, or othercable source, and inserted into an interior of duct 26. Duct 26 can beany of a variety of known ducts, such as polyethylene, suitable forreceiving cable 22 on a long term basis during use of cable 22 fortransmission or conduction of signals. Cable 22 can be any of a varietyof known transmission or conductive cable, including fiber optic cablehaving one or more optical fibers contained therein, and preferablyhaving a circular outer perimeter. Apparatus 20 accepts cable 22 atinlet 36, and cable 22 exits apparatus 20 at outlet 38. Duct 26 extendsfrom apparatus 20 to distal end 30 which can be several hundred feet orless away from apparatus 20, or several thousand feet or more away fromapparatus 20.

Preferably, the motive force generated by apparatus 20 includes apushing force generated by frictional engagement of the cable with amoving drive assembly. Apparatus 20 includes a cable drive assembly 40which frictionally engages cable 22 so as to provide a motive pushingforce. In the preferred embodiment, cable drive assembly 40 ishydraulically driven by a hydraulic pressure source 42 linked by lines42 a to drive assembly 40.

Preferably, the motive force further includes a pulling force generatedby air pressure. Apparatus 20 preferably also includes a cable blowerassembly 44 which allows for air pressure to enter duct 26. A missile 34attached to cable 22 at lead end 32 slideably and sealably closes offduct 26 from the atmosphere sufficient to create a pressure differenceadjacent to missile 34. Cable blower assembly 44 is linked to a bloweror air compressor 46 which generates appropriate air pressure. Air line46 a and valve 46 b (FIG. 2) link blower 46 with cable blower assembly44. Air pressure within duct 26 between missile 34 and apparatus 20causes missile 34 to move toward exit end 30 of duct 26. The airpressure within duct 26 behind missile 34 generates a motive pullingforce at lead end 32 of cable 22.

Apparatus 20 preferably further includes a cable counter assembly 48which monitors the speed of cable 22 during operation. Preferably, cablecounter assembly 48 also monitors the length of cable passing throughapparatus 20 from reel 24.

Apparatus 20 preferably also includes a frame 50, which can be supportedby legs for supporting frame 50 at a convenient level above the ground.Such supporting structure could also include wheels, for convenientlymoving apparatus 20 between locations. Frame 50 also supports cabledrive assembly 40, cable blower assembly 44, and cable counter assembly48. Frame 50 also supports a control assembly 52 (FIG. 2) which monitorsand/or controls operation of various of the components of apparatus 20.Frame 50 allows for the various assemblies to be conveniently used andtransported together as a unit.

Cable blower assembly 44 includes an air block assembly 54 which linksboth cable 22 received from cable drive assembly 40, and the source ofpressurized air from blower 46 with duct 26. Duct mount assembly 56forms a portion of cable blower assembly 44, and securably mounts duct26 to apparatus 20. Adjustment assembly 58 below cable blower assembly44 also forms a portion of cable blower assembly 44, and allows forvertical adjustment of air block assembly 54 and duct mount assembly 56relative to frame 50. The adjustment is with respect to cable driveassembly 40. Such vertical adjustment allows for different diametercables to be installed with apparatus 20. As the diameter of the cableis varied, the location of the central axis of the cable will vary as itexits cable drive assembly 40. Such variance in height is adjusted forin order to allow for proper sealing in airblock assembly 54, as will bedescribed in greater detail below.

Cable drive assembly 40 includes lower and upper tractor driveassemblies 60, 62. Preferably, each is driven by a hydraulic motor, 64,66. Each tractor drive assembly 60, 62 includes a moveable member. In apreferred embodiment, an endless chain in each assembly 60. 62 is drivenby hydraulic motors 64, 66, respectively, so as to frictionally engagecable 22 and apply the motive pushing force to cable 22. In thepreferred embodiment illustrated, tractor drive assemblies 60, 62 opposeeach other and are aligned in the vertical direction. Other moveabledrive members besides opposed endless chains are possible includingwheels and/or belts. Further, the moveable members can be arranged inV-shape, as shown in U.S. Pat. No. 4,285,454, for example.

A lower drive counter 68 monitors movement of lower tractor driveassembly 60, which is indicative of the speed of cable drive assembly40. Such speed monitoring is important for preventing excessive relativespeed between cable drive assembly 40 and cable 22 during slippage.

Cable drive assembly 40 further includes a hold down system, such as ahydraulic clamp cylinder 70 in the preferred embodiment, linked topressure source 42 by line 42 a. This generates a predetermined normalforce on cable 22 between lower and upper tractor drive assemblies 60,62. Some slip is acceptable. Too much slip can cause cable jacketdamage. Too much slip may also limit the usefulness of apparatus 20 ifinsignificant push forces are generated. Duct 26 usually contains someirregularities, joints and bends that can keep cable 22 and missile 34from moving smoothly. Unless an appropriate normal force is generated(not too much slip), the pushing force may be inadequate to overcome theirregularities, and slip may occur too often, causing unnecessary cablejacket damage or insignificant cable push. On the other hand, a normalforce which is too high risks crush damage to the cable, and inadequateslippage, such that column damage will be more likely to occur as cabledrive assembly 40 continues to move cable 22 when cable 22 is beingslowed or stopped within duct 26. When slip does occur under high normalforce loads, cable jacket damage may result. By providing for apredetermined normal force with apparatus 20, predetermined slip levelscan be monitored. This results in an appropriate level of slip, so as tonot cause too many shutdowns of apparatus 20 when cable damage is notsignificantly at risk, but excessive slip is noted, and results in shutoff of apparatus 20 to prevent damage situations.

Apparatus 20 balances the benefits and risks associated with driveassembly 40 which generates a pushing force from a moving memberfrictionally engaged with the cable. Apparatus 20 reduces or avoidscable damage (crush, column, and slippage), but allows for sufficientlylong runs of continuous cable to be installed. Such balance comes frommonitoring and controlling the normal force applied to cable 22, thespeed of cable 22, and the speed of cable drive assembly 40.

As will be described in greater detail below, the control system ofapparatus 20 includes control subsystems for: monitoring and controllingthe speed of lower and upper tractor drive assemblies 60, 62; monitoringthe speed of cable 22; monitoring and controlling system air pressure;and monitoring and controlling the hold down system, such as clampcylinder 70.

Referring now to FIGS. 7-11, further details of cable drive assembly 40are shown. FIGS. 7 and 8 illustrate lower tractor drive assembly 60 ingreater detail. Lower tractor drive assembly 60 includes an endlessdrive chain 80 driven by hydraulic motor 64 having an output shaft 84connected to drive sprockets 86. Motor 64 is mounted to housing 88 atone end. At an opposite end of housing 88, a tensioner 90 is moveablymounted via threaded rod and nut 91 to adjust tension on drive chain 80,and includes rotatably mounted sprockets 92 for supporting drive chain80. Chain 80 includes a plurality of metal chain links 96 with outwardlyfacing pads 98 mounted to mounting flanges 99 of chain 80. Mountingflanges 99 extend outwardly from links 96 on each side of chain 80.

Chain 80 is mounted for movement relative to housing 88 by rotation ofdrive sprockets 86 by motor 64. Elongated region 100 of chain 80 issupported by a center chain guide plate 102 mounted to housing 88.Guides 104 are mounted to center chain guide plate 102 on opposite sidesof chain 80. Guides 104 each include a lip 106 which covers a sideportion of each pad 98 when positioned in the elongated section 100during operation. Preferably, guide plate 102 and guides 104 are madefrom a material with good slide and wear properties, such as plastic.Nylatron plastic is one example.

Referring back to FIG. 4, a counter sprocket 108 is mounted to an end ofsprocket shaft 86 a connected to motor 64. Sprocket 108 is sensed by asensor assembly 112 such as a magnetic pickup which senses sprocketteeth and generates a corresponding signal indicative of moving teeth.Housing 114 (see FIG. 2) protects sprocket 108 and sensor assembly 112.The signal is input to the control system for monitoring movement(speed) of output shaft 84. Monitoring the speed of output shaft 84enables monitoring of the speed of chain 80 directly driven by outputshaft 84. Sensor assembly 112 includes a permanent magnet, a pole-piece,and a sensing coil all contained in a protective case. The teeth ofsprocket 108 (iron, steel or other magnetic material) distort themagnetic flux field passing through the sensing coil and pole-piece,which in turn generates a wave form signal processed by the controlsystem. Other proximity sensors, and other speed sensors can be usedwith apparatus 20, as desired.

Referring now to FIGS. 9 and 10, upper tractor drive assembly 62includes a drive chain 80 a, constructed in a similar manner as drivechain 80 of lower tractor drive assembly 60. Hydraulic motor 66 drivesan output shaft 124 which turns drives sprockets 126. Sprockets 126directly engage drive chain 80 a so as to move drive chain 80 a in asimilar manner as drive chain 80. A housing 128 surrounds chain 80 a,and supports various components including motor 66, and output shaft 124at one end of the housing. An adjustable tensioner 130 at an oppositeend of housing 128 supports rotatable sprockets 132 also supportingdrive chain 80 a . Chain 80 a includes an elongated region 134 supportedby a center chain guide plate 136 mounted to housing 128, and facing inan opposite direction to elongated region 100 of drive chain 80 of lowertractor drive assembly 60. Guide plate 136 is constructed from similarmaterials as guide plate 102. Elongated regions 100, 134 apply a normalforce to cable 22 and the motive pushing force.

Referring now to FIGS. 2-10, the connection is shown between lower andupper tractor drive assemblies 60, 62. The connection includes hydraulicclamp cylinder 70 mounted to housing 88 of lower tractor drive assembly60 at one end and to housing 128 of upper tractor drive assembly 62 atan opposite end. Cylinder 70 includes an extending shaft 142 and aclevis 144 at a distal end. A cylinder mounting bracket 146 mountscylinder 70 to housing 88. Cylinder flange 145 of cylinder 70 mounts tobracket 146 at a bracket mounting flange 147 at a lower end. Bracket 146further includes spaced apart channels 148 and a center projection 150at an upper end.

Structures associated with upper tractor drive assembly 62 cooperatewith clevis 144, and channels 148 and center projection 150,respectively, to mount upper tractor drive assembly 62 for movementSpecifically, a flange 152 extends from housing 128 for receipt ofclevis 144. A pin 154 (FIG. 5) connects clevis 144 to flange 152. Guideblocks 156, 158 extending from housing 128 are spaced apart so as to bereceived in channels 148, with center projection 150 disposedtherebetween. Protective pads 157, 159 extend from guide blocks 156, 158toward bracket 146.

When cylinder 70 is operated so as to move shaft 142 between positions,the clevis link causes corresponding movement of upper tractor driveassembly 62 relative toward or away from lower tractor drive assembly60. The cooperating guide blocks 156, 158 and channels 148 and centerprojection 150 result in alignment of lower and upper tractor driveassemblies 60, 62 at all times.

Clamp cylinder 70 is preferred because of its repeatability and ease ofuse. Manually adjustable clamp systems are possible in accordance withthe invention, but difficulties can arise if the normal force andslippage are not adequately monitored, so as to avoid or reduce thelikelihood of crush damage, column damage, and jacket damage.

Referring now to FIG. 11, an example chain pad 98 is shown in greaterdetail. An outer facing surface 160 defines a central V-shaped channel162. Two oppositely positioned flanges 164 each include two mountingapertures 166 extending therethrough for receipt of fasteners 168 (seeFIGS. 8 and 10) for mounting pad 98 to chain links 96. Preferably, pad90 is made from moldable plastic and includes insert molded lock nuts169. During use, the V-shaped channel 162 receives cable 22, in aself-centering manner.

Referring now to FIGS. 12 and 13, details of cable counter assembly 48are shown in greater detail. Inlet end 170 receives cable 22 to becounted or monitored during introduction into the conduit from a sourceof cable, such as reel 24 illustrated in FIG. 1. Cable counter assembly48 includes a main housing 172 mounted to lower tractor drive assembly60, a generally horizontal front lower support roller 174, and twovertical centering rollers 176. Output roller 178 is positioned beneathcable 22 during use. Output roller 178 is utilized to generateinformation about cable speed, and also preferably cable length. Outputroller 178 includes an output shaft 180, and a sprocket 182 (FIG. 5). Asensor assembly 184 mounted to housing 172 senses sprocket teeth inorder to generate a corresponding signal indicative of moving teeth.Sensor assembly 184 is similarly constructed as sensor assembly 112 formonitoring drive assembly speed. Cable counter assembly 48 relies onfrictional engagement with output roller 178 in order to generateappropriate signals from sensor assembly 184. Top pressure rollers 186apply downward pressure on cable 22 during use so as to achieve properfrictional engagement with output roller 178. Only one pressure roller186 is visible in the drawings on an upstream side of output roller 178.The second pressure roller is located on the downstream side of roller178.

Top pressure rollers 186 are mounted to a movable mounting plate 188connected to a tensioner 190 for adjustment of pressure of pressurerollers 186 on cable 22. Tensioner 190 is preferably spring loaded, soas to prevent excessive pressure on cable 22 between output roller 178,and pressure rollers 186. A block 194 threadably engages a shaft 196. Aspring 198 biases block 194 downwardly. Block 194 moves upwardly againstspring 198 when cable 22 has a kink, or when overcranking of shaft 196occurs by the operator. Pressure rollers 186 are preferably V-shaped soas to help achieve a cable centering feature. Cable 22 exits cablecounter assembly 48 at outlet end 192 where cable 22 is engaged by cabledrive assembly 40. Outlet end 192 mounts to lower tractor drive 60 withsuitable bolts or other fasteners 193 (FIGS. 2 and 3).

Referring now to FIGS. 14-18, further details of cable blower assembly44 are shown. Air block assembly 54 shown in FIGS. 14, 17 and 18receives cable 22 from cable drive assembly 40, and air pressure fromblower 46 and directs both into duct 26. Air block assembly 54 includesupper and lower blocks 200, 202, two locator pins 203, and four mountingbolts 204. Bolts 204 are hingedly connected to lower block 202 adjacenteach corner, and the bolts reside in longitudinal slots through upperblock 200, during use. Threaded nuts 205 secure upper block 200 to lowerblock 202 during use. C-clips 205 a prevent nuts 205 from becomingseparated from bolts 204. Positioned between upper and lower blocks 200,202 are inlet seals 206 which slideably and sealably engage cable 22during use to prevent or restrict air flow out of airblock assemblywhere cable 22 enters. Outlet seals 208 seal the interior of air blockassembly 54 and duct 26 from the atmosphere. A perimeter seal 210 ingroove 211 seals a remainder of air block assembly 54 between inletseals 206 and outlet seals 208 from the atmosphere. An air inlet 216 inlower block 200 connects to blower 46 so as to supply air block assembly54 with the pressurized air.

With particular reference to FIGS. 17 and 18, contained within air blockassembly 54 are inlet insert 212 and outlet insert 214 which allow forsize adjustment to accommodate different cable sizes, and different ductsizes, respectively. Inserts 212 and 214 are removably mounted to lowermain block 215 of lower block 202. Upper block 200 is constructed in asimilar manner including an upper main block 217. Inserts 212, 214 arenot shown in FIG. 14. Each insert 212 and 214 includes inner grooves 206a, 208 a for receipt of seals 206, 208, respectively. Also, lower mainblock 215 includes grooves 212 a, 214 a, and inserts 212, 214 includeprojection rings 212 b, 214 b along the mounting surfaces for secureengagement. Securing fasteners, pins or screws 212 c, 214 c furtheralign and secure inserts 212, 214 to lower main block 215. A similarconstruction is provided for upper main block 217. An outlet or tap line213 allows for system air pressure to be monitored and is connected tocontrol assembly 52. A kit of differently-sized and selectable inserts212, 214 can be provided so as to allow apparatus 20 to be used withdifferent sizes of cable and duct.

Within air block assembly 54, a venturi effect is provided by theinternal configuration of internal chamber 216. Pressure rings 217 areprovided to further seal moving cable 22 from the atmosphere, incombination with seals 206. Rings 217 are believed to developalternatively high and low pressure regions adjacent cable 22, and thisassists to develop a good seal between air block assembly 54 and theatmosphere.

Referring now to FIGS. 15, 17, and 18, duct mount assembly 56 is shownin greater detail. Duct mount assembly 56 includes lower and upperblocks 218 220 held together by two bolts 222 which are hingedlyconnected to lower block 218. Bolts 222 also reside in slots 224 inupper block 220. Threaded nuts 223 secure upper block 218 to lower block220. C-clips 223 a prevent nuts 223 from becoming separated from bolts222. Each block 218, 220 has at least one gripping ring 225 (FIG. 18)for gripping an exterior surface of duct 26 to secure duct 26 to ductmounting assembly 56. Each block 218, 220 has five rings 225 in thepreferred embodiment illustrated. Locator pins 228 assist with properalignment of blocks 218, 220.

To allow for different duct sizes to be used with apparatus 20, grippingring inserts 226, 227 are removably secured to lower and upper mainblocks 219, 221 of lower and upper blocks 218, 220. Insert 226 hasgripping rings 225 positioned on an inside surface, and a projectionring 226 b on an outside surface. Projection ring 226 b resides in agroove 226 a on lower main block 219 for secure mounting together. Asecuring fastener, pin or screw 226 c further aligns and secures insert226 to lower main block 219. A similar construction is provided forupper main block 221 and insert 227. Inserts 226, 227 are not shown inFIG. 15. A similar sizing kit can be provided for inserts 226, 227.

Referring now to FIG. 16, adjustment assembly 58 is shown in greaterdetail. A main mounting block 230 mounts to lower tractor drive 60(FIGS. 2-5). An upper mounting plate 232 is vertically movable relativeto main mounting block 230. 270 Adjustment mechanism 234 allows verticaladjustment of upper mounting plate 232 relative to main mounting block230. Upper mounting plate 232 supports air block assembly 54 and ductmount assembly 56. Such vertical adjustment allows for use of air blockassembly 54 and duct mount assembly 56 with cables of various dimensionswherein the center line would vary relative to lower tractor driveassembly 60. Each of airblock assembly 54 and duct mount assembly 56mount to mounting plate 232 through apertures 236 a, b with suitablescrews or other fasteners. Similarly, main mounting block 230 mounts tolower tractor drive assembly 60 with suitable bolts or other fastenersreceived in apertures 238. Knob 234 a is rotatable to move uppermounting plate 232 up or down along threaded shaft 234 b relative tomain mounting block 230. Clamp 239 locks upper mounting plate 232 intoposition once its height is adjusted.

Refering now to FIG. 19, a cable speed control system 240 of controlassembly 52 is shown schematically. Control system 240 controlsoperation of cable drive assembly 40 so as to terminate operation in thecase of an excessive relative speed difference between cable driveassembly 40 and cable 22. Inputs to a cable speed control module 242include electronic signals from cable sensor assembly 184, and tractordrive sensor assembly 112. Cable speed control system 240 includescircuitry for comparing the sensor inputs so that if a predeterminedspeed difference exists, such as a 15% faster tractor drive speed overthe cable speed, a tractor drive shut off signal is generated. A smallerpercentage difference in the threshold is possible, but it may result inmore frequent, and less necessary system shut offs. A greater percentagedifference is possible, but it may result in less system shut offs, butmore cable jacket damage.

Should control module 242 sense an excessive speed of tractor driverelative to cable 22, control module 242 will activate a hydraulic motorcontrol switch, such as a solenoid 244, thereby shutting down hydraulicmotors 64, 66 and cable drive assembly 40. Should cable speed exceed amaximum threshold or fall below a minimum threshold, the same shut offsignal is generated by control module 242 for solenoid 244. Not only iscable speed monitored, but so is cable distance. Control module 242 hasboth a cable speed display 245, and a cable distance display 246.Control module 242 also includes system electrical power switch 243, andvarious buttons 241 for resetting control system counters and displays,such as displays 245, 246 noted above, for example.

Control module 242 is preferably software controlled and is programmableto accept proximity switch or other monitoring sensor signals indicativeof cable movement and tractor drive movement. Control module 242 isprogrammed accordingly to generate the appropriate display signals, i.e.speed and distance of cable 22, and the appropriate solenoid activationsignal (tractor drive shut off signal) based on the signals receivedfrom the sensors. Any of a variety of conventional control modules 242with programming capability can be used. Control module 242 ispreferably appropriately programmed with desired delays between receiptof signals from the sensors and when a shut off signal is generated sothat only desired shut offs occur. For example, cable 22 may jerk fromtime to time as it is pulled from reel 24. Such jerking motion mayresult in slippage signals from the cable slip sensors. However, with anappropriate time delay programmed into module 242, no system shut offwill occur since this slippage is acceptable. Slippage from jerk isusually only a short term slippage, and typically does not result incable damage. Therefore, there is no need to cause system shut off inthese conditions.

FIG. 2 illustrates an electrical power cord 290 for control module 242,as well as two selectable adaptor plug cords 292, 293 for use withdifferent power supplies in the field. FIG. 2 also illustratesdetachable sensor lines 294, 295 for permitting detachment of controlmodule 242 from the rest of apparatus 20.

Referring now to FIG. 20, a schematic is shown for a hydraulic controlsystem 247 of control assembly 52. Specifically, hydraulic controlsystem 247 includes a hydraulic pump 248 (source 42 in FIG. 1) linked toa fixed relief valve 250, and a pressure-compensated regulator 252.Solenoid 244, and a first directional control valve 254 lead tohydraulic motors 64, 66. A pressure reducer 256, a second directionalcontrol valve (four position, three-way) 258, and two pilot-to-opencheck valves 259 lead to clamp cylinder 70.

Referring now to FIG. 21, frame 50 is shown in greater detail. Variouselongated members 270 a -g are utilized to assemble frame 50. Frame 50supports various components of apparatus 20 including control assembly52 and lower tractor drive assembly 60. Brackets 272 mount to legs (notshown) for supporting members 270 a -g above the ground.

Referring now to FIGS. 22 and 23, various hydraulic control componentsof control assembly 52 are also illustrated with respect to frame 50. Ahydraulic control module 276 includes various gauges 278 for display ofclamp cylinder system hydraulic pressure, system air pressure, and motorsystem hydraulic pressure. Control module 276 also includes a manuallyoperated motor speed control lever 280 for controlling the speed ofmotors 64, 66 via hydraulic directional control valve 254 (FIG. 20).Control module 276 also includes a manually operated up/down controllever 282 for controlling clamp cylinder 70 via hydraulic directionalcontrol valve 258 (FIG. 20). Pressure line port 284 and return line port285, both shown in FIGS. 22 and 23 with protective caps 284 a, 285 aconnect control module 276 to hydraulic pump 248. The various hydrauliclines 286 between motors 64, 66, clamp cylinder 70 and gauges 278 a, care shown at least in part by reference to FIG. 23, and also FIGS. 5 and6, in accordance with the hydraulic schematic of FIG. 20. Control module242 is preferably separate from hydraulic control module 276, andpreferably resides in space 279 on hydraulic control module 276. Bymaking separate modules, module 240 can be detached as desired, such asprotect it from the weather during periods of nonuse.

Referring now to FIG. 24, an example missile 34 is shown in greaterdetail. Missile 34 includes a tip 350, and a connection end 352 forconnecting to cable 22. Typically a swivel is connected to cable 22, andmissile 34 connects to the swivel. Disposed between tip 350 andconnection end 352 is at least one seal 354 for sealing an interior ofduct 26. Missile 34 has two seals 354. Preferably, seals 354 are sizedso that missile 34 generates sufficient pressure to move through duct 26in order to pull cable 22 therethrough, but the seals are not so tightwith duct 26, such that it frequently become stuck when it wouldencounter the common irregularities within duct 26. Silicone rubberdiscs for seals 354 work well. Other sealed missiles besides missile 34are possible for use with apparatus 20.

Apparatus 20 with control assembly 52 prevents damage to cable 22 beinginstalled into the conduit. Damage to fiber optic cables can occur whencable 22 slows down or stops moving in the duct 26. The damage to thecable can be due to column failure, exceeding minimum bend radii, or thepushing device slipping on the cable jacket thus causing wear of thecable jacket. The control system accomplishes this by monitoringslippage by comparing the speed of the pushing device versus actualcable speed. If the control system senses a difference between the twospeeds, it will then stop the pushing device by activating a bypassvalve (solenoid 244). By stopping the pushing device when a speeddifferential (slippage between pusher and cable) is sensed, the wear tothe cable jacket will be minimal. To ensure that slippage between thepushing device and the cable occurs, the cylinder 70 at a predeterminedand fixed pressure controls the amount of clamp force applied to thecable. The amount of down force is directly proportional to the amountof pushing force that can be applied to the cable in accordance with theequation F=μN, where:

μ=coefficient of friction;

N=normal force or clamp force;

F=pushing force.

By limiting the clamping force, the pushing device will slip on thecable before it can exert enough force to cause a column failure. Thisalso ensures that the clamping force does not exceed the compressivelimits of the cable. Since slip damage can occur before a completestoppage of cable 22 occurs, monitoring relative speeds leads to anadvantageous apparatus 20.

The control system also preferably provides two additional safetyfeatures. High speed protection is provided if the cable exceeds aspeed, such as 300 feet/minute (91 meters/minute) in the preferredembodiment, then the control system will stop the pushing device byactivating the bypass valve, thus stopping the cable. The high speedcondition will usually indicate a duct joint failure or out of controlcable situation. Low speed protection is provided if the cable speedfalls below a minimum, such as 25 feet/minute (7.6 meters/minute) in thepreferred embodiment, then the control system will stop the pushingdevice by activating the bypass valve thus stopping the cable. Theunderspeed condition will usually indicate an instant blockage in theduct system. While low speed monitoring is important, low speedmonitoring will not prevent some cable damage situations which areaddressed by the cable slippage monitoring system described above.

Some working examples follow: The chain pad material in the preferredembodiment is a cast polyurethane, having a 95 Durometer shore “A”. Anexample material is compound 6321-A-50D. Example fiber optic cableincludes a polyethylene (medium density) outer jacket. It has beenobserved that an approximate coefficient of friction between these twomaterials is about 0.393. Examples of cable 22 include cable rangingfrom ⅜ inches (10 millimeters) to 1 and ¼ inches (32 millimeters) indiameter. Pirelli Cable Corporation, Outside Plant, Unarmored Loose Tubecable or Customer Premise, Ribbon In Loose Tube cable are appropriatecable types for installation with apparatus 20. In the case of PirelliUnarmored Loose Tube cable, the following data* is provided:

DESIGN PARAMETERS PARAMETER/FIBER RANGES 4-36 38-72 74-96 98-120 122-144146-216 Number of positions 6 6 8 10 12 18 Outside mm 12.0 13.2 14.916.6 18.5 18.9 Diameter in 0.47 0.52 0.59 0.65 0.73 0.74 Cable kg/km 123148 188 232 289 298 Weight lb/1000 ft 83 99 126 156 194 200 Pulling mm18.6 18.6 18.6 20.6 20.6 23.1 Eye 0. D. in 0.73 0.73 0.73 0.81 0.81 0.91Max mtr 12000 12000 12000 12000 10000 10000 Length ft 39370 39370 3937039370 32808 32808 PERFORMANCE SPECIFICATIONS MEASUREMENT UNITSSPECIFICATIONS Bend Radius Dynamic X Cable O. D. 20 Static X Cable O. D.10 Tensile Rating Installation N (lb) 2700 (600)  Residual N (lb) 440(100) Crush Resistance N/cm (lb/in) 220 (125) Temperatures Storage ° C.−50 to +70  ° F. −60 to +160 Installation ° C. −30 to +60  ° F. −20 to+140 Operation ° C. −40 to +70  ° F. −40 to +160

DESIGN PARAMETERS PARAMETER/FIBER RANGES 288-432 Number of Positions 6Outside mm 23.0 Diameter in 0.91 Cable kg/km 460 Weight lb/1000 ft 310Pulling Eye mm 25.6 O.D. in 1.01 Max Length mtr 3000 ft 9842 PERFORMANCESPECIFICATIONS MEASUREMENT UNITS SPECIFICATION Bend Radius Dynamic XCable O.D. 20 Static X Cable O.D. 10 Tensile Rating Installation N (lb)2700 (600) Residual N (lb) 440 (100) Crush Resistance N/cm (lb/in) 440(250) Temperatures Storage ° C. −50 to +70 ° F. −60 to +160 Installation° C. −30 to +60 ° F. −20 to +140 Operation ° C. −40 to +70 ° F. −40 to+160

Data taken from data sheets from Pirelli Cables NorthAmerica—Commrunications Division, 700 Industrial Drive, Lexington, S.C.U.S.A. 29072-3799.

Examples of duct 26 range from 1 inch (25 millimneters) up to 2 inches(51 millimeters) in diameter, as well as SDR 11 and 13.5. Typically,pneumatic pressure is at 135 pounds per square inch (psi) maximum andgenerates at least 175 cubic feet/minute (cfm) (5 cubic meters/minute)minimum and 375 cfm (11 cubic meters/minute) maximum. The hydraulicoperating pressure is typically at 1500 psi (103 bar) maximum, with an 8galons/minute (30 liters/minute) flow maximum and 5 gallons/minute (19liters/minute) flow minimum. Example sensors 112, 184 include Red Lionpart number MP37CA00 magnetic pickups. Example sprockets 108, 182include 60 teeth, with a 2.570 inch diameter, from Madison Electric partnumber 4000-0870. The elongated regions 100, 134 of each drive chain areabout 8 inches (203 millimeters) long and the hydraulic clamp cylinderpressure is set so as to develop about 100 lb/in (176 N/cm) ofcompression force on the cable.

Alternatively, it is to be appreciated that cable conveying apparatus 20of the present invention can be used as a puller which utilizes themotive force in a pulling manner by frictionally engaging cable 22 withdrive assembly 40. The jacket protection features of apparatus 20 areequally advantageous whether apparatus 20 is a puller or a pusher.

It is to be understood, that even though numerous characteristics andadvantages of the invention have been set forth in the foregoingdescription, together with details of the structure and function of theinvention, the disclosure is illustrative only, and changes may be madein detail, especially in matters as such shape, size, and arrangement ofthe parts within the principles of the invention to the full extentindicated by the broad general meaning of the terms which the appendedclaims are expressed.

What is claimed is:
 1. A method of installing cable in a conduitcomprising the steps of: providing a drive assembly for moving the cablein a forward direction; generating a first signal indicative of movementof the drive assembly; generating a second signal indicative of movementof the cable; comparing the first and second signals over time; andgenerating a drive assembly shut off signal if relative speeds of thedrive assembly and the cable exceed a predetermined difference.
 2. Themethod of claim 1, further comprising the steps of providing the cablewith a missile sealably engaged with an inner wall of the conduit, andapplying air pressure to the missile so as to generate a pull force onthe cable.
 3. The method of claim 1, further comprising the step ofgenerating a drive assembly shut off signal if the second signalindicates a cable speed above a predetermined maximum threshold value,or a cable speed below a predetermined minimum threshold value.